This invention relates to portable apparatus used for geophysical exploration for buried objects such as mines, relics and minerals and, in particular, to improved means to avoid the effect of erroneous signals in hand-held devices of this type.
Present portable detector apparatus operate based on the transmission of microwave energy into the ground and subsequent reception of the returning signal. A buried object will affect the energy levels at the receiving antenna in a fashion which differs from the response over a homogeneous medium. However, another factor which will affect the receiving antenna response level is whether the antenna is parallel to the ground. If the antenna is tilted with respect to the ground, a change in signal level will be observed at the receiving antenna. This is due to distance differences to the ground between transmitting dipoles in certain systems, and antenna energy decoupling in other systems. The net result is an unwanted increase in signal levels proportional to the amount of tilt. In portable detector systems, the antenna is mounted at the end of a rigid handle which is swung in an arc by the operator. Normal operation will result in the antenna being tilted at the endpoints of the arc where the operator has stopped and is starting his motion in an opposite direction. As a consequence, false signals are received at these endpoints which can result in objects going undetected or in erroneous indications of the presence of a buried object.